Sign base



FIG. 1 is a front perspective view of a sign base showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines shown in the figures are provided for the purpose ofillustrating an environment only and form no part of the claimed design.

CLAIM The ornamental design for a sign base, as shown and described.